A new reforming process based on CH4 decomposition using a hydrogen-permeating membrane reactor

A new reforming process was studied using Ni/SiO₂ with a hydrogen-permeating membrane reactor. Nickel catalyst supported on SiO₂ is highly active for CH₄?H₂O?O₂ reaction in membrane reactor and the reaction close to CH₄+0.35O₂+1.3H₂O→CO₂+3.3H₂ proceeds at 873 K. Since the selectivity to carbon and CO₂ increased and decreased with decreasing contact time respectively, it is considered that the reaction was started by decomposition of CH₄ followed by oxidation of C and water shift reaction. Therefore, the reaction mechanism was different from so-called autothermal reforming (ATR) reaction.     

Partial Oxidation of Methane into Syngas with Oxygen Permeating Ceramic Membrane Reactors

Partial oxidation of methane (CH₄ +1/2O₂ CO + 2H₂) is considered as an alternative reforming reaction to steam reforming for production of syngas. This reaction is a slightly exothermic reaction and produces syngas of H₂/CO = 2, which is suitable for the synthesis of hydrocarbon or methanol. In this paper, the catalytic partial oxidation of CH₄ with a membrane reactor using oxygen permeating ceramic, in particular, LaGaO₃-based oxide, is reported. Supported Ni or Rh catalysts are active and selective for this reaction. On the other hand, a mixed ionic and electronic conducting (MIEC) ceramic membrane is useful for obtaining pure oxygen from air when the gradient in oxygen partial pressure is obtained. As for a MIEC membrane, mixed electronic–oxide ionic conductors of Fe- or Co-based perovskite oxides are widely investigated. However, the improvement in stability in a reducing atmosphere is critically required for the MIEC membrane for the application to the membrane reactor for CH₄ partial oxidation. Perovskite oxides of LaGaO₃ doped with Sr for a La site and a Fe, Co, or Ni for a Ga site, respectively, are promising as the oxygen-separating membrane for CH₄ partial oxidation because of high stability in a reducing atmosphere as well as high permeability of oxygen. The partial oxidation of CH₄ with solid oxide fuel cells (SOFCs) is also described. Simultaneous generation of electrical power and syngas is demonstrated by the fabricated fuel cell type reactor using a LaGaO₃-based oxide electrolyte.     

Hydrogen‐Permeable Tubular Membrane Reactor: Promoting Conversion and Product Selectivity for Non‐Oxidative Activation of Methane over an Fe©SiO2 Catalyst

Non‐oxidative methane conversion over Fe©SiO₂ catalyst was studied for the first time in a hydrogen (H₂) permeable tubular membrane reactor. The membrane reactor is composed of a mixed ionic–electronic SrCe_0.7Zr_0.2Eu_0.1O_3?δ thin film (≈20 μm) supported on the outer surface of a one‐end capped porous SrCe_0.8Zr_0.2O_3?δ tube. Significant improvement in CH₄ conversion was achieved upon H₂ removal from the membrane reactor compared to that in a fixed‐bed reactor. The Fe©SiO₂ catalyst in the H₂ permeable membrane reactor demonstrated a stable ≈30 % C₂₊ single‐pass yield, with up to 30 % CH₄ conversion and 99 % selectivity to C₂ (ethylene and acetylene) and aromatic (benzene and naphthalene) products, at the tested conditions. The selectivity towards C₂ or aromatics was manipulated purposely by adding H₂ into or removing H₂ from the membrane reactor feed and permeate gas streams.     

The oxidative stream reforming of methane to syngas in a thin tubular mixed-conducting membrane reactor

The oxidative stream reforming of methane (OSRM) to syngas, involving coupling of exothermic partial oxidation of methane (POM) and endothermic steam reforming of methane (SRM) processes, was studied in a thin tubular Al₂O₃-doped SrCo_0.8Fe_0.2O_3−δ membrane reactor packed with a Ni/γ-Al₂O₃ catalyst. The influences of the temperature and feed concentration on the membrane reaction performances were investigated in detail. The methane and steam conversions increased with increasing the temperature and high conversions were obtained in 850–900 °C. Different from the POM reaction, in the OSRM reaction the temperature and H₂O/CH₄ profoundly influenced the CO selectivity, H₂/CO and heat of the reaction. The CO selectivity increased with increasing the temperature or decreasing the H₂O/CH₄ ratio in the feed owing to the water gas shift reaction (H₂O + CO → CO₂ + H₂). And the H₂ selectivity based on methane conversion was always 100% because the net steam conversion was greater than zero. The H₂/CO in product could be tuned from 1.9 to 2.8 by adjusting the reaction temperature or H₂O/CH₄. Depending on the temperature or H₂O/CH₄, furthermore, the OSRM process could be performed auto-thermally with idealized reaction condition.     

From CH4 reforming with CO2 to pyrolysis over a platinum catalyst

At temperatures up to 1100°C, CH₄ and CO₂ react over a Pt wire to give mainly the reforming product CO, even at a CH₄/CO₂ ratio of 4.3. But if coke is present on the wire, the dominant reaction becomes the pyrolysis of CH₄ to form mainly C₂H₂ and C₆H₆. Thus, surface carbon poisons the reforming reaction and is autocatalytic for CH₄ pyrolysis. Higher temperatures and larger CH₄/O₂ ratios favor the formation of coke and the pyrolysis reaction. Molecular oxygen and, to a lesser extent, water have the opposite effect.     

费托合成CeO2助Co/SiO2催化剂的失活

在固定床反应器上考察了原粒度(1～3mm)CeO2助Co/SiO2催化剂的费托反应性能,提出了催化剂失活的机理,并采用程序升温还原、X射线衍射和X射线光电子能谱对催化剂进行了表征.结果表明,在1.5MPa,488K和400h-1条件下进行的300h稳定性实验中,原粒度CeO2助Co/SiO2催化剂上的CO平均转化率达到41%,液态烃选择性达到85%,液态烃中C10 烃的质量含量占88%以上.反应器出口的催化剂中有少量的CoO和Co2SiO4生成.催化剂的失活过程受动力学控制而非热力学控制,催化剂的失活机理为:高分散的纳米Co离子在反应器出口高水蒸气压力的作用下,以CoO为中间物种,与水合SiO2作用生成Co2SiO4,即Co H2O→CoO H2,SiO2 H2O→OSi(OH)2,2CoO OSi(OH)2→Co2SiO4 H2O.     

Reforming of CO<Subscript>2</Subscript>-Containing Natural Gas Using an AC Gliding Arc System: Effect of Gas Components in Natural Gas

The objective of the present work was to study the reforming of simulated natural gas via the nonthermal plasma process with the focus on the production of hydrogen and higher hydrocarbons. The reforming of simulated natural gas was conducted in an alternating current (AC) gliding arc reactor under ambient conditions. The feed composition of the simulated natural gas contained a CH₄:C₂H₆:C₃H₈:CO₂ molar ratio of 70:5:5:20. To investigate the effects of all gaseous hydrocarbons and CO₂ present in the natural gas, the plasma reactor was operated with different feed compositions: pure CH₄, CH₄/He, CH₄/C₂H₆/He, CH₄/C₂H₆/C₃H₈/He and CH₄/C₂H₆/C₃H₈/CO₂. The results showed that the addition of gas components to the feed strongly influenced the reaction performance and the plasma stability. In comparisons among all the studied feed systems, both hydrogen and C₂ hydrocarbon yields were found to depend on the feed gas composition in the following order: CH₄/C₂H₆/C₃H₈/CO₂ > CH₄/C₂H₆/C₃H₈/He > CH₄/C₂H₆/He > CH₄/He > CH₄. The maximum yields of hydrogen and C₂ products of approximately 35% and 42%, respectively, were achieved in the CH₄/C₂H₆/C₃H₈/CO₂ feed system. In terms of energy consumption for producing hydrogen, the feed system of the CH₄/C₂H₆/C₃H₈/CO₂ mixture required the lowest input energy, in the range of 3.58 × 10⁻¹⁸–4.14 × 10⁻¹⁸ W s (22.35–25.82 eV) per molecule of produced hydrogen.     

Application of non-thermal atmospheric pressure ac plasmas to the carbon dioxide reforming of methane

Methane conversions of 11.9%, yields of hydrogen as high as 23.3% and energy yields of 1.0 mol H₂/kWh have been achieved from CO₂ reforming of CH₄ in non-thermal, atmospheric pressure plasma reactors with Pt coated electrodes. Two reactors have been studied. A novel fan type reactor consisting of a movable rotor and immobile stator produced the highest yields in contrast to a tube type (silent discharge) reactor with a glass dielectric barrier. Conversions, yields of hydrogen and energy yields (expressed as mol H₂/kWh) were studied for CO₂/CH₄ concentrations of 1.1% and 5.0% in He as a function of flow rate and input voltage. Hydrogen yields are observed to increase as the input voltage is increased from 411 V to 911 V and the flow rate is decreased from 100 cc/min to 30 cc/min. Energy yields vary only slightly with input voltage and flow rate. Hydrogen yields show little dependence on CO₂/CH₄ concentrations, but energy yields are approximately five times greater for the 5.0% mixture than the 1.1% mixture. Selectivities to H₂, CO, coke, and low molecular weight hydrocarbons were also evaluated and compared to data obtained without CO₂ in the feed. Hydrogen selectivities of nearly 100% were obtained, with small amounts of ethane and propane as the only observed side products and the selectivites were approximately the same whether CO₂ was present or absent in the mixture. However, the reaction proceeds much more cleanly when CO₂ is present, producing CO. The syngas product has an H₂ : CO ratio of 1.5 with the fan type reactor and 0.67 with the tubular reactor. In the absence of CO₂, coke is the main carbonaceous product. Under all conditions studied the fan type reactor demonstrated higher methane conversions (up to 11.9%) and selectivities to hydrogen.     

NiO-CaO materials as promising catalysts for hydrogen production through carbon dioxide capture and subsequent dry methane reforming

In this work, CaO-NiO mixed oxide powders were evaluated as consecutive CO_2 chemisorbents and catalytic materials for hydrogen production thought the CH_4 reforming process. Between the NiO impregnated CaO and CaO-NiO mechanical composite, the first one presented better chemical behaviors during the CO_2 capture and CH_4 reforming processes, obtaining syngas(H_2+ CO) as final product. Results showed that syngas was produced at two different temperature ranges, between 400 and 600 °C and at T 800 °C, where the first temperature range corresponds to the CH_4 reforming process but the second temperature range was attributed to a different catalytic reaction process: CH_4 partial oxidation. These results were confirmed through different isothermal and cyclic experiments as well as by XRD analysis of the final catalytic products, where the nickel reduction was evidenced. Moreover, when a CO-O_2 flow was used during the carbonation process a triple process was achieved:(i) CO oxidation,(ii) CO_2 chemisorption and(iii) CH_4 reforming. Using this gas flow the hydrogen production was always higher than that obtained with CO_2.     

Marked Effect of Various Supports and Additives Upon Liquid Phase Methanol Reforming with Water over Supported Group 8–10 Metal Catalysts

The support effects (SiO₂, TiO₂, Al₂O₃, MgO, CeO₂ and ZrO₂) as well as addition effect of group 6b and 7b elements were studied over various supported group 8–10 metal catalysts. Basic oxide support improved the selectivity to CO₂ and acidic support suppressed the catalytic activity and selectivity. Among the investigated catalysts Pt–Mo/TiO₂ was the most active catalysts, whereas Ir–Re/SiO₂ was the most selective catalysts for H₂ and CO₂ formation. The mechanism of the liquid phase methanol reforming reaction over silica supported Pt–Ru catalyst was studied by kinetic investigations. The rate of H₂ formation over Pt–Ru/SiO₂ catalysts was more than 20 times faster than that over Pt/SiO₂ catalysts with high selectivity for CO₂ (72.3%), indicating a marked addition effect of Ru. In the case of HCHO–H₂O reaction over Pt–Ru/SiO₂, the H₂ formation rate was five times larger than that in the CH₃OH–H₂O reaction but selectivity to CO₂ was only 4%. On the contrary, in the HCOOCH₃–H₂O and HCOOH–H₂O reactions, both high activity and selectivity were observed over Pt–Ru/SiO₂. These results clearly indicate that the CO₂ formation does not proceed via HCHO decomposition and following water gas shift reaction.     

析因设计结合响应面法分析甲烷干重整过程中通过形成碳纳米管进行二氧化碳减排(英文)

A factorial experimental design was combined with response surface methodology(RSM) to opti-mize the catalyzed CO2 consumption by coke deposition and syngas production during the dry re-forming of CH4. The CH4 /CO2 feed ratio and the reaction temperature were chosen as the variables, and the selected responses were CH4 and CO2 conversion, the H2 /CO ratio, and coke deposition. The optimal reaction conditions were found to be a CH4 /CO2 feed ratio of approximately 3 at 700 °C, producing a large quantity of coke and realizing high CO2 conversion. Furthermore, Raman results showed that the CH4 /CO2 ratio and reaction temperature affect the system's response, particularly the characteristics of the coke produced, which indicates the formation of carbon nanotubes and amorphous carbon.     

助剂对NiMgAl催化剂的结构和甲烷二氧化碳重整反应性能的影响(英文)

向担载镍基催化剂NiMgAl中添加助剂(Co,Ir或Pt)制备了三种助剂促进型催化剂,通过氢气程序升温还原(H2-TPR),CO2/CH4程序升温表面反应(CO2/CH4-TPSR)和CO2程序升温脱附(CO2-TPD)等方法对催化剂进行表征.助剂对催化剂性能的影响通过甲烷干重整实验进行评价.添加少量的Pt或Ir助剂可以降低Ni活性组分的还原温度和提高反应性能.添加助剂的样品与原始NiMgAl催化剂相比能够降低反应的活化能,添加Co或Ir助剂的催化剂与NiMgAl催化剂相比活化能有了明显的降低.NiMgAl催化剂的活化能为51.8 kJ·mol-1,添加Pt助剂的NiPtMgAl催化剂活化能降至26.4 kJ·mol-1.NiMgAl催化剂中添加Pt助剂制备的催化剂具有较好的催化活性和较低的活化能.CH4-TPSR和CO2-TPSR结果表明添加Pt助剂可以在更低的温度下(与NiMgAl催化剂相比)提高CH4的活化能力,并在催化剂表面形成更多的碳物种.CO2-TPD结果显示,添加助剂的催化剂与NiMgAl样品相比在反应温度区间内增加了CO2的吸附/脱附量.     

Catalytic Oxidation of Methane to C2‐C4 Hydrocarbons over CeO2 Promoted W‐Mn/SiO2 Catalysts at Higher Pressure

CeO₂‐promoted Na‐Mn‐W/SiO₂ catalyst has been studied for catalytic oxidation of methane in a micro‐stainless‐steel reactor at elevated pressure. The effect of operating conditions, such as GHSV, pressure and CH₄/O₂ ratio, has been investigated. 22.0% CH₄ conversion with 73.8% C₂‐C₄ selectivity (C₂/C₃/C₄ = 3.8/1.0/3.6) was obtained at 1003 K, 1.5 × 10⁵ h^?;1 GHSV and 1.0 MPa. The results show: Elevated pressure disadvantages the catalytic oxidation of methane to C₂‐C₄ hydrocarbons. Large amounts of C₃ and C₄ hydrocarbons are observed. The unfavorable effects of elevated pressure can be overcome by increasing GHSV; the reaction is strongly dependent on the operating conditions at elevated pressure, particularly dependent on GHSV and ratio of CH₄/O₂. Analyses by means of XRD, XPS and CO₂‐TPD show that CO₂ produced from the reaction makes a weakly poisoning capacity of the catalyst; information of changeful valence on Ce and Mn was detected over the near‐surface of the Ce‐Na‐W‐Mn/SiO₂ catalyst; the existence of Ce³⁺/Ce⁴⁺ and Mn²⁺/Mn³⁺ ion couple supported that the reaction over the catalyst followed the Redeal‐Redox mechanism. Oxidative re‐coupling of C₂H₆ and CH₄ in gas phase or over surface of catalyst produces C₃ or C₄ hydrocarbons.     

Surface Reaction Kinetics of the Oxidation and Reforming of CH4 over Rh/Al2O3 Catalysts

An 48‐step sur face reaction mechanism with thermodynamic consistent kinetic data is presented for the catalytic conversion of the gaseous chemical system H₂/O₂/H₂O/CO/CO₂/CH₄ over Rh/Al₂O₃ catalysts. Total and partial oxidation as well as steam reforming and dry reforming of methane over Rh catalysts is studied experimentally and numerically at varying temperature and composition. The results are used to extend the kinetic schemes we developed for H₂ oxidation, CO oxidation kinetics, and the water‐gas‐shift reactions in former studies. Aside from the experiments in a stagnation‐flow reactor presented here, we modeled a number of experiments from the literature to test the newly established kinetic scheme.     

Combining electrolysis with thermocatalysis for dry reforming of methane in a naturally stratifying liquid alloy-salt catalytic system

Dry reforming of methane (CH₄) with carbon dioxide (CO₂) is an attractive technology for producing value-added syngas and mitigating greenhouse gas emission. However, this process usually requires high energy input due to the intrinsic inertness of CH₄ and CO₂. Besides, the widely investigated solid Ni-based catalysts typically suffer from coking and sintering issues, leading to degradation in catalytic performance. Liquid alloys and molten salts are emerging as promising catalytic materials for CH₄ dry reforming. In this work, we combine electrolysis with thermocatalysis for CH₄ dry reforming in a naturally stratifying liquid alloy-salt system, which achieves effective and stable catalytic performance under relatively mild operation conditions. The conversions of CH₄ and CO₂ reach 37% and 95%, respectively, in a bubble column reactor comprising Ni–Bi alloy and LiNaCO₃ during constant current electrolysis at 1.5 A and 900 °C. The selectivities of H₂ and CO were maintained at 85% and 92%, respectively. Ab initio molecular dynamics simulation shows that the oxides of both Ni and Bi promote the C–H bond dissociation. Therefore, the electrochemical process combine electrolysis with thermocatalysis in the liquid alloy-salt system represents a promising approach to achieving effective and stable CH₄ dry reforming.     

High-Efficient Conversion of CO<Subscript>2</Subscript> in AC-Pulsed Tornado Gliding Arc Plasma

An AC-pulsed tornado gliding arc plasma was employed for CO₂ conversion via CO₂ decomposition and dry reforming reactions. A stable and high-efficient constant arc length discharge mode was obtained in this plasma reactor. And then, CO₂ conversion was studied under this discharge mode. In the case of CH₄/CO₂ = 0, CO₂ was converted to CO and O₂ via the CO₂ decomposition reaction. Energy efficiency of 29 % was attained at CO₂ conversion of 6 %. With strong reducing agent CH₄ added into CO₂, the main contributor of CO₂ conversion changed from CO₂ decomposition to dry reforming of CH₄. Conversions of CH₄ and CO₂, energy efficiency and energy cost changed sharply at CO₂/CH₄ ratios lower than 1/4, while they changed slowly at CH₄/CO₂ ratios above 1/4. In the case of CH₄/CO₂ = 2/3, energy efficiency of 68 % and syngas energy cost of 1.6 eV/mole were achieved at CH₄ conversion of 29 % and CO₂ conversion of 22 %.     

Syngas production in a novel perovskite membrane reactor with co-feed of CO2

Partial oxidation of methane（POM） co-fed with CO₂ to syngas in a novel catalytic BaCo_0.6Fe_0.2Ta_0.2O_3-δ oxygen permeable membrane reactor was successfully reported.Adding CO₂ to the partial oxidation of methane reaction not only alters the ratio of CO/H₂,but also increases the oxygen permeation flux and CH₄ conversion.Around 96%CH₄ conversion with more than 93%CO₂ conversion and 100%CO selectivity is achieved,which shows an excellent reaction performance.A steady oxygen permeation flux of 15 mL/（cm² min） is obtained during the 100-h operation,which shows good stability as well.     

Dry Reforming of Methane by DC Spark Discharge with a Rotating Electrode

A novel type of plasma reactor having a rotating electrode is proposed for CO₂ reforming of methane without catalyst at room temperature and atmospheric pressure. Results indicated that employing rotating ground electrode leads to a stable discharge for any period of time. Effects of feed composition, feed flow rate, applied power and electrodes separation on the carbon dioxide and methane conversions as well as the products selectivity were investigated. Increasing CO₂/CH₄ molar ratio in the feed favors the reagents conversion and consequently promotes the formation of hydrogen and carbon monoxide. If the target product is hydrogen, it is proposed to operate the reactor at CO₂/CH₄ = 1 molar ratio and if the target product is carbon monoxide then CO₂/CH₄ = 3 molar ratio is the preferred option for feed composition. This reactor system has advantages of stable operation and high conversion ability. Also, the obtained syngas with flexible molar ratio of H₂ to CO is suitable for vast industrial applications.     

Oscillations during partial oxidation of methane to synthesis gas over Ru/Al2O3 catalyst (Special column of methane transformation, Article)

Oscillations in temperatures of catalyst bed as well as concentrations of gas phase species at the exit of reactor were observed during the partial oxidation of methane to synthesis gas over Ru/Al₂O₃ in the temperature range of 600 to 850 °C. XRD, H₂-TPR and in situ Raman techniques was used to characterize the catalyst. Two types of ruthenium species, i.e. the ruthenium species weakly interacted with Al₂O₃ and that strongly interacted with the support, were identified by H₂-TPR experiment. These species are responsible for two types of oscillation profiles observed during the reaction. The oscillations were the result of these ruthenium species switching cyclically between the oxidized state and the reduced state under the reaction condition. These cyclic transformations, in turn, were the result of temperature variations caused by the varying levels of the strongly exothermic CH₄ combustion and the highly endothermic CH₄ reforming (with H₂O and CO₂) reactions (or the less exothermic direct partial oxidation of methane to CO and H₂), which were favored by the oxidized and the metallic sites, respectively. The major pathway of synthesis gas formation over the catalyst was via the combustion-reforming mechanism.     

Methane production from synthesis gas using a mixed culture ofR. rubrum M. barkeri,and M. formicicum

The components of synthesis gas, CO, H₂, and CO₂, may be converted into CH₄ biologically through either acetate or H₂/CO₂ as intermediates. Of these two routes, conversion through H₂/CO₂ is preferred. This paper presents results of mixed-culture studies employing the photosynthetic bacteriumR. rubrum for converting CO to CO₂ and H₂ by the water gas shift reaction and two methanogens,M. formicicum andM. barkeri, for converting CO₂ and H₂ into CH₄. Results are presented for triculture operation in two types of reactors, the packed bubble column and the trickle-bed reactor.